Direction indicating systems for road vehicles

ABSTRACT

A direction indicating system for a road vehicle has a direction indicator switch operating in the usual manner, but having a resistor in series with it. Control means is provided operable by the voltage across said resistor for increasing the frequency of operation if a lamp fails.

United States Patent 91 Williams July 17, 1973 DIRECTION INDICATINGSYSTEMS FOR ROAD VEHICLES [75] inventor: David Gordon Williams,

Birmingham, England [73] Assignee: Joseph Lucas (Industries) Limited, I

Birmingham, England [22] Filed: Jan. 12, 1972 [21] App]. No.: 217,176

[30] Foreign Application Priority Data Jan. 13, 1971 Great Britain1,590/71 s21 U.S.Cl 340/81 F, 340/251 511 Int. Cl ..B60q 1/38 58FieldotSearch 340/79, 80,8112,

[56] References Cited UNITED STATES PATENTS 3,263,119 7/1966 Scholl340/81 R X 3,329,868 7/1967 Domann et a1 340/81 R UX 3,593,264 7/1971Atkins 340/251 X 3,604,949 9/1971 Conzelmann et a1. 340/80 X 3,576,4444/1971 Roberts 340/81 F X 3,665,207 5/1972 Sieber 340/81 R X PrimaryExaminer-John W. Caldwell Assistant Examiner-Kenneth N. LeimerAttorney-John C. Holman et al.

[57] ABSTRACT A direction indicating system for a road vehicle has adirection indicator switch operating in the usual manner, but having aresistor in series with it. Control means is provided operable by thevoltage across said resistor for increasing the frequency of operationif a lamp fails.

1 Claim, 1 Drawing Figure PATENTED JUL 1 7 I975 1 DIRECTION INDICA'IINGSYSTEMS FOR ROAD VEHICLES This invention relates to direction indicatingsystems for road vehicles.

A system according to the invention comprises in combination a directionindicator switch having a movable contact with an inoperative positionand a pair of operative positions in which the direction indicator lampson opposite sides of the vehicle respectively are energised, supplymeans operable when the movable contact is in an operative position tosupply current intermittently at a predetermined frequency to thedirection indicator lamps selected by the direction indicator switch, aresistor in series with said movable contact, and control means operableby the voltage across said resistor for increasing said predeterminedfrequency if a selected direction indicator lamp fails.

The accompanying drawing is a circuit diagram illustrating one exampleof the invention.

Referring to the drawing, there are provided positive and negativesupply lines 11, 12, the line 11 being connected through the ignitionswitch 13 of a vehicle to the positive terminal of a vehicle battery 14,and the line 12 being connected to the negative terminal of the vehiclebattery, the negative terminal being earthed.

Connected into series between the lines 11, 12 are three resistors 15,16 and 17, the junction of the resistors l6 and 17 being connectedthrough a resistor 18 to the base of an n-p-n transistor 19, thecollector of which is connected through a resistor 20 to the line 11 andis further connected to the base of an n-p-n transistor 21, the emittersof the transistors 19 and 21 being connected to the line 12 through aresistor 22. The collector of the transistor 21 is connectedto the line11 through a coil 23 of a relay. The coil 23 being bridged by a resistor24 and serving when energised to close a normally opened contact 25which is connected to the line 11 through a resistor 26, and is furtherconnected to a direction indicator switch 27. The switch 27 has amovable contact which is engageable with either of a pair of fixedcontacts to energise the left-hand direction indicator lamps 28 or theright-hand direction indicator lamps 29 of the vehicle.

The junction of the resistor 26 and contact 25 is connected to theemitter of a p-n-p transistor 31, the collector of which is connected tothe line 12 through a resistor 32, and is further connected through adiode 33 to the junction of a pair of resistors 34, 35 connected inseries between the lines 11, 12. The junction of the resistors 34, 35 isconnected through a capacitor 36 to the junction of the resistors 16,17, and the base of the transistor 31 is connected through a resistor 37to the emitter of an n-p-n transistor 38, the collector of which isconnected to the line 11 and the base of which is connected to the line11 through a resistor 39, and is further connected through resistors 41and 42 in series to the line 12. The junction'of the resistors 41 and 42is connected to the base of the transistor 31, and the movable contactof switch 27 is connected to the junction of the resistors and 16.

When the ignition switch 13 is closed with the switch 27 in the positionshown, the transistor 19 is turned on by current flow through theresistors 15, 16 and 18 and so the transistor 21 is off and the coil 23is deenergised. The transistor 38 and its associated resistors 37, 39,41 maintain the base of the transistor 31 at a small but constantnegative potential with respect to line 11, the characteristics of thetransistor 38 serving to compensate for temperature variations, and theresistor 37 compensating for variations in the supply voltage. Since thecoil 23 is de-energised, the contact 25 is open, and the emitter of thetransistor 31 is connected to the line 11, so that the transistor 31 isfully conductive, and the diode 33 conducts so that the junction of theresistors 34, 35 is substantially at the potential of the line 11. Thejunction of the resistors 16, 17 is at a potential determined by theratio of the combined resistance of the resistors 15 and 16 to theresistance of the resistor 17, so that the capacitor 36, althoughinitially discharged, will rapidly charge to a potential which is asubstantial part of the voltage between the lines 11, 12. However, whenit is desired to indicate a turn, the switch 27 is operated to connectthe junction of the resistors 15 and 16 to the line 12 through thebulbs. The capacitor 36 now charges further by way of two parallelpaths, one containing the resistor 17, and the other containing theresistor 16, the switch 27 and one of the pairs of lamps 28, 29. Thecurrent flowing through the lamps at this stage is insufficient toenergise them. Charging of the capacitor 36 gradually reduces the basecurrent of the transistor 19, until a point is reached at which thetransistor 19 turns off and the transistor 21 turns on, at which pointthe coil 23 is energised and the contact 25 closes to energise theselected pair of lamps 28 or 29. As soon as the transistor 21 conducts,the emitter potential of the transistor 19 is raised by virtue of thecurrent flowing through the resistor 22, so ensuring that the transistor19 is turned off rapidly.

As soon as the relay contact 25 closes to energise the selected lamps 28or 29, the capacitor 36 can discharge through the resistor 16, thecontact 25 and the resistor 26, and when the capacitor 36 has dischargedto a predetermined level, the transistor 19 will turn on again, turningoff the transistor 21, so that the contact 25 opens and the lamps arede-energised. When the contact 25 opens, the potential at the junctionof the resistors 34 and 35 will return to approximately the potential ofthe line 11. The cycle is then repeated, assuming that the switch 27 isstill operated, and the lamps 28 or 29 flash at a rate which isdetermined by the length of time taken for the capacitor 36 to dischargesufficiently to enable the transistor 19 to turn on again. Thearrangement is such that provided both lamps 28 or 29 are operatingsatisfactorily, then the current flowing through the resistor 26 reachesa level such that the emitter potential of the transistor 31 is reducedto such a value that the transistor 31 ceases to conduct. When thetransistor 31 is turned off in this way, the diode 33 will not beconductive, and the potential at the junction of the resistors 34 and 35will be reduced to a value which is considerably less than the potentialof the line 11. The conduction of the transistor 19 is determined by thepotential at the junction of the resistors 16 and 17, which in turn isdetermined both by the charge on the capacitor 36 and by the state ofconduction of the transistor 31. The capacitor 36 must discharge to apredetermined level before the transistor 19 turns on again and it willbe seen that the amount by which the capacitor 36 must discharge isequal to the increased voltage drop across the resistor 22 when thetransistor 21 conducts, plus the reduction in voltage at the junction ofthe resistors 34, 35 occasioned by the turning off of the transistor 31.The period of time taken for the capacitor 36 to discharge determinesthe operating frequency of the system, but in the event that one of thelamps 28 or 29 fails, then when the contact 25 is closed, the currentflowing through the resistor -26 is insufficient to turn off thetransistor 31, so that the diode 33 is still conductive, and thejunction of the resistors 34 and 35 remains at a potential close to thepotential of the line 11. ln these circumstances, the capacitor 36 onlyhas to discharge by a voltage equal to the increase voltage drop againstthe resistor 22, and consequently the transistor 19 turns on again farmore quickly than in the case when both lamps 28 or 29 are operatingsatisfactorily. Thus, the frequency of operation of the system increasessubstantially giving a warning to the driver.

A further switch can be provided for operating all the lamps 28 and 29simultaneously to give a hazard warning and it will be seen that sincethe transistor 31 will be off if all four lamps are operating, then thefrequency of operation is substantially unaffected by the simultaneousflashing of all four lamps.

I claim:

l. A direction indicating system for a road vehicle, comprising incombination first and second supply lines for connection to a vehiclebattery, a first resistance chain connected across said supply lines, asecond resistance chain connected across said supply lines, a capacitorcoupling a point in the first resistance chain to a point in the secondresistance chain, a switching circuit connected to a point in saidsecond resistance chain, said switching circuit having a first state anda second state and being driven from the first state to the second statewhen the voltage across said capacitor reaches a predetermined level,and being driven back from the second state to the first state when thevoltage across said capacitor falls to a second predetermined level, theswitching circuit when in said second state serving to energise a relaycoil, a direction indicator switch having a movable contact with aninoperative position and a pair of operative positions in which itcompletes a circuit across the supply lines to the direction indicatorlamps on opposite sides of the vehicle respectively, the circuitcompleted by the movable contact of the direction indicator switchincluding a normally open contact of said relay and a resistor, atransistor having its base and emitter coupled to the supply lines andsaid resistor so that said transistor is normally conductive but turnsoff if said movable contact is in an operative position unless one ofthe selected direction indicator lamps fails, means coupling saidtransistor to the first resistance chain to change the potential at oneside of said capacitor when the transistor conducts, and a connectionfrom the movable contact of the direction indicator switch to the secondresistance chain, the arrangement being such that with the movablecontact in an operative position and said transistor turning off, thecapacitor charges and discharges to cause the lamps to flash at apredetermined frequency, but if a lamp fails the transistor remainsconductive and acts on said first resistance chain to modify the amountby which the capacitor must discharge before the switching circuitdeenergises the relay coil, so increasing the operating frequency of thesystem.

1. A direction indicating system for a road vehicle, comprising incombination first and second supply lines for connection to a vehiclebattery, a first resistance chain connected across said supply lines, asecond resistance chain connected across said supply lines, a capacitorcoupling a point in the first resistance chain to a point in the secondresistance chain, a switching circuit connected to a point in saidsecond resistance chain, said switching circuit having a first state anda second state and being driven from the first state to the second statewhen the voltage across said capacitor reaches a predetermined level,and being driven back from the second state to the first state when thevoltage across said capacitor falls to a second predetermined level, theswitching circuit when in said second state serving to energise a relaycoil, a direction indicator switch having a movable contact with aninoperative position and a pair of operative positions in which itcompletes a circuit across the supply lines to the direction indicatorlamps on opposite sides of the vehicle respectively, the circuitcompleted by the movable contact of the direction indicator switchincluding a normally open contact of said relay and a resistor, atransistor having its base and emitter coupled to the supply lines andsaid resistor so that said transistor is normally conductive but turnsoff if said movable contact is in an operative position unless one ofthe selected direction indicator lamps fails, means coupling saidtransistor to the first resistance chain to change the potential at oneside of said capacitor when the transistor conducts, and a connectionfrom the movable contact of the direction indicator switch to the secondresistance chain, the arrangement being such that with the movablecontact in an operative position and said transistor turning off, thecapacitor charges and discharges to cause the lamps to flash at apredetermined frequency, but if a lamp fails the transistor remainsconductive and acts on said first resistance chain to modify the amountby which the capacitor must discharge before the switching circuitde-energises the relay coil, so increasing the operating frequency ofthe system.